1. Field of the Invention
The present invention relates to a Wavelength Division Multiplexing (WDM) optical transmission system. More particularly, to an optical source used for testing an optical component and an optical fiber-based optical source.
2. Description of the Related Art
As WDM optical transmission systems are developed that are capable of exponentially extending transmission bandwidth, a multi-lambda source is required to constitute an optical transmission network, as well as test an optical device and a system. In particular, to reduce costs required for constructing a subscriber network, the development of the multi-lambda source is an important problem to be solved.
The requirements of the multi-lambda source are as follows: (1) the multi-lambda source should provide the number of wavelengths corresponding to the number of wavelength bands to be used; (2) the multi-lambda source should output high power and provide uniform optical intensity according to a wavelength; (3) the multi-lambda source should provide a good Optical Signal to Noise Ratio (OSNR); and (4) polarization characteristics should be excluded where the multi-lambda source is used to test the WDM optical transmission system and its components.
Conventional multi-lambda source splits a wide spectrum of Amplified Spontaneous Emission (ASE) light generated by an Erbium Doped Fiber Amplifier (EDFA) into narrow spectrums using an optical filter. However, such a conventional multi-lambda source is not efficient, since much of the ASE light not corresponding to the optical filter wavelengths is consumed.
FIG. 1 is a view illustrating a configuration of a conventional multi-lambda source using an Arrayed Waveguide Grating (AWG). The multi-lambda source includes an ASE source 110, an optical isolator 120, an AWG 130, an EDFA 140 and an optical attenuator 150.
The ASE source 110 outputs ASE light having a wide spectrum. The optical isolator 120 passes the ASE light received from its back and cuts off light received from its front. The AWG 130 has a pass band of a number of wavelengths, and outputs an optical signal of a plurality of channels by filtering the ASE light. A channel configures an optical signal and includes light of a predetermined wavelength. The EDFA 140 amplifies the optical signal and then outputs the amplified optical signal. The optical attenuator 150 adjusts an intensity of the amplified optical signal by attenuating the amplified optical signal.
Disadvantageously, however, the conventional multi-lambda sources have limitations due to the line width of each wavelength constituting the pass band being wide in the AWG 130 and the intensity of a channel varying with the wavelength.
FIG. 2 is a view illustrating a configuration of a conventional multi-lambda source using FBGs (Fiber Bragg Gratings). The multi-lambda source includes an ASE source 210, an optical circulator 220 and a plurality of FBGs 230 arranged in series.
The ASE source 210 outputs ASE light having a wide spectrum, and the optical circulator 220 outputs the ASE light inputted through a first stage to a second stage. Light inputted into the second stage is outputted to a third stage. Each FBG 230 reflects only light having a predetermined wavelength (center wavelength) and then passes light of the remaining wavelength. Center wavelengths of the FBGs 230 constitute a reflection band, the light reflected from the FBGs 230, i.e., channels, constitutes the optical signal, and the optical signal is inputted into the second stage of the optical circulator 220.
The conventional multi-lambda source as described above has a number of limitations, for example, significant costs are incurred and insertion loss is increased because such a source should have the predetermined number of FBGs arranged in series to constitute a desired reflection band. Further, efficiency of such a source is deteriorated due to much of the ASE light not included in the reflection band is consumed.